Positive displacement pumps are used to pressurize fluid. One such pump is a multi-piston compressor utilized to pressurize gas by reciprocating movement of pistons within cylinders in a cylinder block. The cylinders are positioned in spaced relation circumferentially and also radially outwardly from the center of rotation of a piston drive. The pistons in such a pump are driven by what is referred to as a swashplate which is a plate secured to a shaft for rotation with the shaft with the plane of the plate being positioned at an angle relative to perpendicular to the axis of rotation of the shaft. The pistons are connected to the swashplate such that rotation of the swashplate will effect reciprocating motion of the pistons within the cylinders. Pivotal shoes are provided for the pistons to compensate for the change in angular relation between the swashplate and the longitudinal axis of the pistons during rotation of the swashplate. Pumps of this type can be used to pressurize both liquids and gases and are well known in the art. They are commonly used as hydraulic pumps and as air conditioning compressors.
The assembly of such pumps has been complicated because of the need to assemble the pistons into the cylinder block as a unit with the swashplate. One means of assembling such a compressor involved the use of fingers that are extended through the cylinders in the cylinder block to grip a respective piston to retain the pistons in position while pulling the pistons into the cylinders and maintaining the pistons aligned with the cylinders. The fingers are thin metal on the order of a few thousands of an inch thick. These fingers damage easily and can also damage pistons and cylinders which can lead to premature wear and failure of the pump and more importantly result in assembly apparatus downtime for repair.
In current manufacturing of air compressors, the parts are closely fit with very tight tolerances particularly at the point of engagement of piston shoes to the swashplate. Rather than custom make the components, the components are sorted into size categories. The thickness of a particular swashplate is known and its location on the automated assembly line is also known. The appropriate number of pistons is selected and gaged to determine the size of shoes needed to provide the proper fit between the shoes and the swashplate. Tolerances are sometimes maintained in the micron range for fit. The appropriately sized shoes are then installed in the pistons and the pistons with the installed shoes are then queued at a known location on the assembly line. The assembly apparatus then ensures that the appropriate piston set is assembled to the selected swashplate at an assembly station. By being gaged upstream of the assembly station, assumptions are made that both the piston set and matched swashplate arrive at the assembly station in the proper order. Further, if the assembly apparatus malfunctions, care must be taken in order to ensure the proper sequence of piston sets and swashplates are maintained to ensure subsequent proper assembly.
There is therefore a need for an improved and simplified apparatus and method for assembling multi-piston pumps.
The present invention relates to a method and apparatus for assembling multi-piston pumps that utilize a swashplate to effect reciprocating linear motion of the pistons in the cylinders. The apparatus includes a conveyor that is operable to receive and transport pistons while retained in cradles. Shoes are fitted in sockets in the pistons and retained in the sockets during movement to an assembly station. At the assembly station, the pistons are positioned circumferentially about the swashplate and retained in their respective positions in the conveyor by retainers. When at the assembly station the shoes are retained in their respective sockets by the swashplate. A drive is provided to move the conveyor and the pistons to the assembly station and once the pistons are placed in cylinders in a cylinder block the drive will retract the conveyor from its compressor assembly location to its fill location.
The method involves placing a plurality of pistons in cradles along a conveyor. The pistons have grooves at the bottom end (swashplate end) with sockets on opposite sides of the groove facing toward one another for the receipt of shoes in the sockets. A gap is maintained between the shoes that is slightly larger than the thickness of the swashplate. The gap dimension is held to very close tolerance. A swashplate is mounted at an assembly station with the swashplate being in line with the gaps between the shoes. The conveyor is wrapped around the swashplate with the swashplate being received in the gaps between the shoes. The pistons are positioned at predetermined locations both circumferentially around the swashplate and radially from the center of rotation of the swashplate so that they are in line with the cylinders in a cylinder block. After the pistons are in position, the cylinder block is moved to the pistons with the pistons each being simultaneously inserted into a respective cylinder. The conveyor is then retracted and separated from the pistons after which the pistons are each fully inserted into their respective cylinder and the swashplate shaft is inserted into a bearing for rotation relative to the cylinder block.
The present invention also relates to a method of assembling pumps by gaging the various components at the assembly station to thereby eliminate the need for tracking the various matched components through the assembly machine. Gaging at the assembly station simplifies the construction and operation of the apparatus as well as its repair and maintenance during down times.
Other objects and features will be in part apparent and in part pointed out hereinafter.